Cocaine addiction alters how people perceive rewards and make it more difficult to learn from mistakes, reveals a new study.
Scientists analyzing the brains of addicts found the drug disrupts the dopamine neurons that govern how we perceive and learn from rewards.
And though cocaine addicts maintain similar expectations of rewards, their dopamine neurons send out far weaker signals when these rewards are actually received.
It is hoped the study, from researchers based in the United States, can be used to inform and improve current addiction treatment.
It is already well-documented that cocaine addiction can impact multiple aspects of dopamine signaling in the brains of both humans and animals.
However, it is as yet unclear whether certain paths of the dopamine signaling pathway are more important than others.
Rather than errors in dopamine signaling, addictive behavior is believed to be due to disruptions to ‘reward prediction error’ – a system that calibrates future expectations based on past experiences by comparing expected rewards with actual rewards as encoded by dopamine neurons in the brain.
Few studies have thus far been able to accurately demonstrate the impact of cocaine use on reward prediction error in humans.
The research team, from Rutgers University and the Icahn School of Medicine at Mount Sinai in the United States, used fMRI scanning to examine neural activity in the brains of cocaine addicts and healthy control subjects whilst each performed a simple decision-making task.
The task involved choosing between a ‘safe’ monetary reward or gambling on a ‘risky’ reward, which carried a chance of being either much higher or lower in value than the safe option.
The research team compared brain activity during two phases of prediction error calculation: the expected phase, while participants were making their decision and anticipating the resulting reward; and the actual reward phase, when participants were presented with the outcome of their decision.
The scientists found that those with cocaine addiction displayed reduced prediction error responses, which was consistent with studies on animals.
The study, published in the journal Neuron, also discovered that though signals of reward expectation were similar for both groups, the signal for received reward was weaker for those with cocaine addiction.
This weakened reward signal was visible in the ventral striatum – the brain region where prediction error is processed – and reduced activity was also visible in the orbitofrontal cortex – a brain region involved in integrating the prediction error signal to inform future behavior.
Neuroscientist and addiction expert Dr Rita Goldstein, from the Icahn School of Medicine at Mount Sinai, says the research supports the perception of addiction as a disorder instead of a choice or weakness.
“Our results support the medical model of addiction as a disorder of the brain that deserves treatment,” Dr Goldstein explains.
“Addiction is a disorder and not a choice or a moral weakness.”
Dr Anna Konova, a neuroscientist at Rutgers University, added: “If you’re not tracking the reward signal appropriately, it makes it much harder to disengage from something that’s no longer rewarding.
“We found evidence that people with chronic cocaine addiction have reduced prediction error responses, and this difference seems to be caused by differences in the subjective perception of received reward.
“The reduced reward signal seems to propagate to other regions of the brain that would receive this information to then update your expectations for the next time you encounter this same situation.”
The researchers additionally demonstrated that people with addiction were more likely to gamble with riskier options when compared to those who weren’t addicted.
They further showed that this risk tolerance was more apparent in those who had begun using cocaine at an earlier age – pointing towards potential predisposing factors for developing addiction.
The American researchers hope their study can help inform and improve addiction treatments going forward.
“Our findings suggest that interventions that boost the perception of received rewards might be a valuable component of addiction treatment,” Dr Goldstein said.
“Understanding the brain mechanisms behind addiction is also extremely valuable for the public and for the person experiencing addiction.”
The research team will next endeavor to understand how dysregulation of reward signaling changes during different stages of addiction and recovery, and whether reward perception is involved in other types of substance disorder, such as in addiction to opioids like heroin.
Dr. Goldstein added: “We want to understand how this signal changes through the progression of recovery, or as a function of different stages of addiction to understand whether it’s really driven by chronic cocaine exposure or something that comes on earlier, maybe even before you start substance use.”
Produced in association with SWNS Talker
